The present invention relates generally to detonators. More specifically, the present invention relates to a semiconductor bridge ("SCB") initiated detonators for explosive materials.
Most electro-explosive (e.g., bridge wire or metal foil) devices contain a small metal bridge wire heated by a current pulse from a firing set with nominal output voltages ranging from one to several tens of volts. In order to obtain environmental tolerance along with acceptable shelf-life, electro-explosive devices are usually designed with hermetically sealed housings with electrical feed-throughs. Additionally, thermally-initiated devices must be able to withstand reasonable, unintended currents without firing because relatively-low energies are required to cause firing of the devices. Any current will produce some heating of the bridge wire and most designs of thermally-initiated devices have limited capability to transport this heat away from the thermally-sensitive explosive material. Heat transport from the bridge wire to an exoergic material next to the wire is a thermally-conductive process that produces an explosive output, typically a few milliseconds after the start of the current pulse. "No fire" (the maximum current that can be applied to the bridge wire for a specified period of time without causing ignition) and all-fire (the minimum current level required for reliable ignition) current levels are dependent upon the exoergic material and the physical configuration of the explosive device.
The inexpensive and reliable ignition of explosive materials is a desirable goal for both economic and safety reasons. U.S. Pat. No. 4,708,060, Semiconductor Bridge (SCB) Igniter, of Bickes, Jr. et al. depicts a semiconductor bridge ("SCB") igniter that satisfies this goal. The SCB igniter comprises a small, doped polysilicon or silicon layer formed on a non-conducting substrate (e.g., silicon or sapphire). The heavily doped, approximately one ohm, SCB is formed between two spaced conductive lands (e.g., metal such as aluminum) and in contact with an explosive material. The length of the SCB is determined by the spacing of the conductive lands; SCBs are nominally 100 .mu.m long and 380 .mu.m wide and the doped layer is typically two .mu.m thick. The conductive lands provide a low ohmic contact to the underlying doped layer. SCB resistance at ambient conditions is typically one ohm. Header wires are bonded to the conductive lands and the electrical feed-throughs on the explosive header posts to permit a current pulse to flow from land-to-land along the current flow axis of the SCB.
U.S. Pat. No. 4,976,200, A Tungsten Bridge for the Low Energy Ignition of Explosive and Energetic Materials , of Benson et al., depicts a tungsten SCB that includes a substrate covered by a layer of an insulating material such as silicon dioxide, a semiconductor bridge on the surface of the layer of the insulating material, and a pair of conductive lands deposited over the semiconductor bridge. The semiconductor bridge includes a first layer of an insulating material, which comprises silicon, in contact with the substrate and a second layer, which includes tungsten, selectively deposited only over the entire first layer. A pair of electrical conductors are each connected to one of the lands and a power source is connected to the electrical conductor for supplying current to the lands.
The SCB is easily designed to not fire when a "no fire" current is applied, but to fire when a higher "fire" current is applied. As disclosed in U.S. Pat. No. 4,708,060, application of a 15 amps, 15 .mu.s current pulse through the SCB produces a plasma discharge that ignites the explosive material at a relatively slow rate. Such ignition is suitable for actuators, gas generators, and rocket motors, but is not fast enough for other applications.
In some applications, high-explosive powders are initiated, as opposed to ignited, by the direct output from a bridge wire or metal foil (see for example, exploding bridge wire ("EBW") devices). These devices can often use more stable explosive materials, which is an important safety consideration.
U.S. Pat. No. 4,862,803, Integrated Silicon Secondary Explosive Detonator, of Nerheim et al. depicts a detonator device for primary or secondary explosive materials comprising an integrated circuit consisting of a silicon wafer substrate on which an epitaxial layer of a desired thickness is first grown, followed by a covering insulating oxide layer. U.S. Pat. No. 4,862,803 claims back-etching the silicon wafer to define a barrel for a flyer plate.
U.S. Pat. No. 4,840,122, Integrated Silicon Plasma Switch, of Nerheim depicts a switch device for use in detonation systems and for one-time use in conducting very high currents. The switch device comprises a silicon substrate on which is deposited an amorphous silicon or polysilicon strip extending as a bridge between first and second lands deposited on the silicon substrate. Also deposited on the same substrate on opposite sides of the bridge and spaced from it are a set of high-voltage contacts. Unlike the present invention, U.S. Pat. No. 4,840,122 depicts the use of an extra pair of electrodes. When a high voltage is applied across the contacts, no current flows until a trigger current is made to flow through and vaporize the bridge.
Statutory Invention Reg. No. H 1,366, SCB Initiator, of Bickes, Jr., et al. depicts a detonator device for high-explosive materials initiated by mechanical impact of a flying plate, the detonator device includes a cylindrical barrel, a layer of flyer material mechanically covering the barrel at one end, and a SCB igniter that includes a pair of electrically-conductive pads connected by a SCB. The SCB is in operational contact with the layer through the barrel to detonate the explosive material. Unlike the present invention, the detonator device described in Statutory Invention Reg. No. H 1,366 does not teach the necessary header wire orientation, which is critical to the operation of the detonator.
The present invention uses a high-current pulse to cause a SCB to function similar to an EBW detonator. The present invention provides a low-inductance firing system to discharge into a SCB to initiate it, similar to an EBW detonator. Also, the present invention uses a SCB for direct and very prompt initiation of a high-explosive material. In one embodiment, the present invention provides a laser to arm an undoped SCB for direct initiation. The embodiments disclosed herein have a current conduction scheme, e.g., header wires connecting the SCB lands to the header posts of explosive devices, that is substantially parallel to the direction of current flow through the SCB.